Wall boxes are hollow structures defining an air flow channel or channels that are used to carry air or exhaust from inside a building (residential or commercial) to the outside. They are usually placed near a window to carry air from rooms that need venting, such as a kitchen, washroom, laundry room, or the like, to the outside.
In the construction of a building, a wall box is typically mounted to an exterior wall, or to a component of the wall such as a window frame assembly. Once mounted, the wall box is covered with a moisture-proof and insulating material and tape is used to seal the edges of the material. The material, thus sealed, prevents moisture from escaping from the wall box, such as moisture resulting from condensation on the exterior of the wall box during normal use conditions, or from air flowing through the wall boxes. Such moisture, if it escapes, can lead to mould and other moisture-related problems. The insulating property of the material allows the building to be heated and cooled more efficiently.
A conventional method for moisture-proofing and insulating a wall box is to use a spray gun to apply polyurethane foam to the exterior of the wall box, save for a flanged opening to which another vapour barrier is attached. Upon spraying, the foam expands and solidifies into an uneven and irregular mass. A problem with this conventional method is that it is very labour intensive as multiple applications of foam may be required to ensure that there are no holes in the sprayed foam that would undermine the insulating and moisture-proofing properties of the material. The final product also has an uneven and irregular surface which makes it challenging to apply a further vapour barrier in the form of plastic sheeting in such a way as to provide a proper seal.
Further challenges are experienced by subsequent tradesmen, i.e. drywall tradesmen, who must, in some situations, cut the foam in order to make space to install the drywall. When the foam is cut, holes can reappear which would undermine the integrity of the foam structure.